The key here was not just making people do something in order to get the schwag, it was making them do something that made the person feel slightly awesome. That's an interaction they're going to remember. A good lesson for any marketing exercise.
The regular expression solution is easily my favorite. The way it shifts the board to find all the diagonals is a great gotcha, it took me a few minutes to understand what the heck was going on.
Thanks! I'm really pleased with how deceptively simple it looks on the surface. Once you actually try to read the code, though....
Swag. Shit We All Get. Schwag is something you get at an altogether entirely different sort of venue.